1. Field of the Invention
Rotary switches are switched on and off by the rotational movement of a rotary handle. They are in the form of at least two parts and have a rotatable switching means arranged in a housing and a rotary knob having a coupling element which can be pushed into or onto the switching means. They are used, for example, as electrical switches in construction machines, electronic data processing systems and various other apparatuses. They may be in the form of simple electrical on/off switches or in the form of complicated three-way or multiway switches.
2. Description of the Prior Art
However, rotary switches are also used in other technical areas. Thus, for example, U.S. Pat. No. 5,060,486 discloses a thermostat controller for a refrigerator and freezer. This thermostat controller is intended for establishing four permanent control ranges and has a rotary knob with four rib-like stop elements and a stationary final control element which is arranged on the thermostat housing and can be brought into contact with the stop elements of the rotary knob. In order to set a specific control range, the final control element is therefore set between, in each case, two stop elements, for which purpose the rotary knob is pulled out axially, then turned to the desired positionxe2x80x94i.e. to the position corresponding to the control range to be selectedxe2x80x94and then pushed back onto the thermostat housing.
The present invention relates to an electrical rotary switch for switching electrical signals on and off, in particular an electrical key switch.
In the case of known key switches, the coupling element which can be pushed into or onto the electrical switching means is a key or a key bit which, during use, is inserted into a slot provided for it in the switching element. In order to protect the switching means from soiling, the key or the key bit is additionally used in a cap-like rotary handle or rotary knob which is mounted on, or pushed onto, the housing of the switch element. In these cases, the latter preferably projects so far out of the front plate of the switch panel that an effective connection between the switch element and the coupling element or the key of the rotary knob is possible.
The known key switches have no sufficient securing means to prevent overturning of the key. In extreme casesxe2x80x94especially with the application of excessive forcexe2x80x94this leads to the key bit breaking off or to damage to the switching mechanism, which then generally results in a tedious and expensive replacement of the entire switch.
It is the object of the present invention to provide a rotary switch in which undesirable overturning of the key is not possible.
This object is achieved, according to the invention, by a rotary switch comprising rotatable switching means arranged in a cylindrical or conical housing and a rotary knob which is provided with a coupling element insertable into the switching means wherein the rotary switch is secured to prevent overturning of the coupling element by ribs which are arranged on the rotary knob and on the outside of the front plate or on said housing and can come into contact with one another.
The novel rotary switch has a housing having a rotatable switching means and a rotary knob having a coupling element which can be pushed into or onto the switching means. According to the invention, undesired overturning of the coupling element, preferably in the form of a key, is prevented by ribs which are arranged on the rotary knob and on the front plate carrying the rotary switch or on said housing and which are capable of coming into contact with one another. The invention is thus distinguished essentially in that, when the rotary knob is in the pushed-in or pushed-on state, it engages a stationary stop rib and thus limits the rotational movement of the key to a rotational range specified in advance.
An advantageous embodiment of the invention envisages that an annular securing disc having a stop rib projecting from the front plate is arranged on the front plate and that the rotary knob has a projecting, arc-shaped rib which, when the rotary knob is in the pushed-on state, can be made to engage the stop rib of the securing disc. In this case, the overturning prevention device according to the invention is therefore formed in such a way that it can also be readily adapted to or mounted on known and already installed rotary switches of the type mentioned at the outset.
Another advantageous embodiment of the invention envisages providing the key switch with at least two rotary knobs which in turn, owing to a different type of rib design, permit different rotational movements for the actuation of a rotary switch at least in the form of a three-way switch. This in turn makes it possible to provide the operator with different rotary buttons depending on his task, which rotary buttons in turn permit 1, 2 or more switching operations on one and the same switch element and can thus be used as so-called authorization keys.